This is incredibly valuable feedback directly from the intended audience, provided for free. Awesome!

A middle click is the middle mouse button, typically clicking with the scroll wheel these days. I don't use a Mac touchpad/mouse but Google says it can be done with a triple finger tap, possibly requiring a setting to be enabled under Accessibility.

I'm glad tools exist to find more details about terminology that I don't already know. It's always a balance to decide what needs explaination and what a reader probably already knows.